If you want cheap and fun get a 9mm. It may be about to surpass .357 and .45acp as my favorite caliber.
For a high quality, accurate, fun and affordable gun you can't beat a CZ 75. Since you are willing to go to $550 check out the CZ 85 Combat and CZ 75 SA depending on how you'll use it. Check out the
CZ forum .
Ruger makes some very good guns. They are very reliable and durable but they aren't particularly nice. I liked my P89 that I had and it was incredibly reliable but it isn't the most refined gun out there. The CZ is just as good, much nicer and about the same price (maybe less).
Any Taurus METAL framed gun is good (stay away from the polymer framed autos). The PT 92/99/100/101 (9mm with fixed sights, 9mm with adjustable, .40 fixed, .40 adjustable) is basically the same as the Beretta 92 but with a framed mounted safety and with a better safety (it works as a decocker AND allows "cocked and locked", condition one, carry). The PT 911/940/945 (9mm, .40, .45acp) are also very nice, a bit smaller, and have the same safety.
This isn't your first gun right? If it was you should also look towards a revolver. Heck, even if it isn't you should also consider a revolver.
Edited: Meant to say stay away from the Taurus POLYMER guns NOT alloy guns. opps.